Wednesday, October 27, 2010

The human body varies in many different ways between and within populations. Among all the variations, the size and shape of the body are of the most interesting. According to the article “Variation in Human Body Size and Shape” written by Christopher Ruff, “Mean body mass (weight) varies by 50% or more, within sex, in a worldwide sampling of populations…Variation in height is smaller (about 10%)…Variation in breadth is larger (about 25%),” (211).

One of the main factors that contributes to body mass and shape is geographic location. As latitudes increase, so does body mass. As people migrate further from the equator, temperatures decrease and body mass increases in order to retain more heat. As for body shape, it is also greatly influenced by climate. In colder climates, humans generally have shorter limbs and wider bodies whereas humans in warmer climates tend to have long limbs and a more lean body shape. This is due to surface area of the body and the ability to retain heat. In colder climates, shorter limbs and wider bodies mean less surface area to lose heat whereas in warmer climates, more surface area is better to more efficiently cool the body (220). Other factors, such as nutrition, contribute to body shape as well. Malnourishment leads to smaller body size than those that receive adequate nutrition, but the most important factor in body size and shape is geographic location.

Height also varies in living humans, although it does not generally depend on geographic location. As mentioned above, height varies by about 10% in living humans. However, it is also important to look at height changes over time as the human body has evolved. Since about 50,000 years ago, there has been a decrease in body size, caused by multiple factors. “These include technological improvements that decreased the selective advantage of a larger body (which is also metabolically expensive to maintain), a decline in nutritional quality, climatic factors (adaptation to a warming environment), and reduced gene flow (inbreeding),” (216). These factors have led to smaller bodies than those of our Neanderthal relatives. However, over the past few hundred years, there has been a slight upward trend in body size in some areas of the world (generally in more developed areas), due to improved nutrition and health overall (217).

Body size and shape vary greatly in living humans and over evolutionary relatives. While there are multiple explanations for these trends, geographic location and nutrition seem to be the most commonly agreed upon reasons for the variation that exists today.